WASHINGTON - The enrollment records for a significant portion of the Americans who have chosen health plans through the online federal insurance marketplace contain errors - generated by the computer system - that mean they might not get the coverage they're expecting next month.

The errors affect roughly one-third of the people who have signed up for health plans, according to two government and health-care industry officials. The White House disputed the figure but declined to provide its own.

The mistakes include failure to notify insurers about new customers, duplicate enrollments or cancellation notices for the same person, incorrect information about family members, and mistakes involving federal subsidies. The errors have been accumulating since HealthCare.gov opened two months ago, even as the Obama administration has been working to make it easier for consumers to sign up for coverage, the government and industry officials said.

Figuring out how to clean up the backlog of errors and prevent similar ones in the future is emerging as the new imperative if the federal insurance exchange is to work as intended. The problems were the subject of a meeting Monday between administration officials and a new "Payer Exchange Performance Team" made up of insurance industry leaders.

The idea that one-third of the enrollment records are flawed "doesn't accurately reflect the picture of what's happening right now," White House senior communications adviser Tara McGuinness said.

"We've got a team of experts already working closely with issuers to make sure that every past and future 834 is accurate. We're confident they'll succeed," McGuinness said. The 834s are nightly enrollment forms sent to insurers to tell them who their new customers are.

Some of the errors in the past forms were generated by the way people were using the system, another senior official on the project said, such as clicking twice on the confirmation button or moving backward and forward on the site.

Through more than a dozen bug fixes over the last week, the team has managed to reduce the instances of when data was not generated on 834 forms from 3 percent last week to 0.5 percent now, according to senior officials.

The heightened attention to enrollment errors follows a five-week technical blitz to improve consumers' ability to use the site.

Federal health officials announced Sunday that they had met that goal.

According to a government official with knowledge of the federal exchange, an internal report Monday showed that nearly 149,000 individuals have completed the enrollment process through the new online system.

Insurers have been fretting about the problems involving the enrollment records for weeks, both publicly and in private conversations with the White House.

Health-Care Site Sees Surge of Users

The federal health website received 375,000 visitors on Monday by noon, the White House says.

That's a surge in use on the first business day since Obama administration officials declared that the government's beleaguered online insurance service was now able to accommodate a vast majority of users.

White House spokesman Jay Carney said the White House had been expecting such a rush of traffic on Monday on HealthCare.gov.

Consumers were still experiencing delays. Carney said that users were placed in a queue and advised when to return for speedier service.    - APEndText